Image forming apparatus including a fixing device comprising a first nip pad and second nip pad and method for controlling image forming apparatus

Abstract

An image forming apparatus includes a first fixing member, a second fixing member, and a controller. The second fixing member includes a first nip forming member and a second nip forming member each configured to nip an endless belt in combination with the first fixing member to form a nip region. A first end face on a first-fixing-member side of the first nip forming member is located closer, than a second end face on a first-fixing-member side of the second nip forming member, to the first fixing member. The controller is capable of executing a first printing process performed in a nip region formed between each of the first nip forming member and the second nip forming member and the first fixing member, and a second printing process performed in a nip region formed between only the first fixing member and the first fixing member.

What is claimed is: 
     
       1. An image forming apparatus comprising:
 a first fixing member including a roller; 
 a second fixing member configured to nip a sheet in combination with the first fixing member, the second fixing member including:
 an endless belt; 
 a first nip forming member and a second nip forming member which are each configured to nip the endless belt in combination with the first fixing member to form a nip region in which the sheet is nipped between the endless belt and the roller, the first nip forming member having a first end face that faces the first fixing member, and the second nip forming member having a second end face that faces the first fixing member; and 
 a single holder configured to support the first nip forming member and the second nip forming member in such a manner that the first nip forming member and the second nip forming member are moved together; 
 
 a heater that heats the first fixing member or the second fixing member; 
 a guide configured to support the holder in a manner that permits the first nip forming member and the second nip forming member supported by the holder to move with respect to the first fixing member in a predetermined direction toward or away from the first fixing member; 
 a spring configured to bias the second fixing member toward the first fixing member; 
 a cam configured to move the second fixing member in the predetermined direction; and 
 a controller, 
 wherein the controller is capable of executing:
 a first printing process in which printing is performed with the holder located in a position where both of the first nip forming member and the second nip forming member nip the endless belt in combination with the first fixing member, and 
 a second printing process in which printing is performed with the holder located in a position where the first nip forming member nips the endless belt in combination with the first fixing member, but the second nip forming member does not nip the endless belt in combination with the first fixing member, 
 
 wherein the first end face is located closer to the first fixing member than the second end face, in a state where the second printing process is being executed 
 wherein the first nip forming member and the second nip forming member are made of rubber, and 
 wherein the first nip forming member is softer than the second nip forming member and located upstream of the second nip forming member in a direction of conveyance of the sheet. 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein, in the first printing process, a biasing force of the spring is exerted on the first nip forming member and the second nip forming member, and
 wherein, in the second printing process, the biasing force of the spring is not exerted on the first nip forming member and the second nip forming member. 
 
     
     
       3. The image forming apparatus according to  claim 1 , further comprising a frame configured to support ends of the first fixing member, in an axial direction of the first fixing member,
 wherein the frame includes a groove as the guide, the groove being elongate in the predetermined direction. 
 
     
     
       4. The image forming apparatus according to  claim 1 , further comprising an arm configured to be rotatable, and biased by the spring to press the second fixing member against the first fixing member. 
     
     
       5. The image forming apparatus according to  claim 4 , wherein the cam is configured such that:
 in a state in which the cam is not in contact with the arm, the second fixing member is located in a position where both of the first nip forming member and the second nip forming member nip the endless belt in combination with the first fixing member, and 
 in a state in which the cam is in contact with the arm, the second fixing member is located in a position where the first nip forming member nips the endless belt in combination with the first fixing member, but the second nip forming member does not nip the endless belt in combination with the first fixing member. 
 
     
     
       6. The image forming apparatus according to  claim 5 , wherein the controller is configured to:
 keep the cam from contacting the arm during execution of the first printing process, and 
 bring the cam into contact with the arm during execution of the second printing process. 
 
     
     
       7. The image forming apparatus according to  claim 1 , wherein the first nip forming member and the second nip forming member are respectively supported on surfaces of the holder located at the same positions in the predetermined direction. 
     
     
       8. The image forming apparatus according to  claim 1 , wherein the first nip forming member and the second nip forming member are rectangular parallelepiped members. 
     
     
       9. The image forming apparatus according to  claim 1 , wherein the first nip forming member is located apart from the second nip forming member in a direction of conveyance of the sheet, and the first nip forming member and the second nip forming member are respectively biased forward directions away from each other by a holder spring. 
     
     
       10. The image forming apparatus according to  claim 1 , wherein the controller is configured to:
 execute the first printing process if a type of sheet for printing is plain paper, and 
 execute the second printing process if the type of sheet for printing is envelope. 
 
     
     
       11. A method for controlling an image forming apparatus including a fixing device, the fixing device comprising:
 a first fixing member; 
 a second fixing member configured to nip a sheet in combination with the first fixing member, the second fixing member including:
 an endless belt; 
 a first nip forming member and a second nip forming member which are each configured to nip the endless belt in combination with the first fixing member to form a nip region in which the sheet is nipped between the endless belt and the first fixing member, the first nip forming member having a first end face that faces the first fixing member, and the second nip forming member having a second end face that faces the first fixing member; and 
 a single holder configured to support the first nip forming member and the second nip forming member in such a manner that the first nip forming member and the second nip forming member are moved together; 
 
 a heater; and 
 a guide configured to support the holder in a manner that permits the first nip forming member and the second nip forming member supported by the holder to move with respect to the first fixing member in a predetermined direction toward or away from the first fixing member; 
 the method comprising executing:
 a first printing process in which printing is performed with the holder located in a position where both of the first nip forming member and the second nip forming member nip the endless belt in combination with the first fixing member, and 
 a second printing process in which printing is performed with the holder located in a position where the first nip forming member nips the endless belt in combination with the first fixing member, but the second nip forming member does not nip the endless belt in combination with the first fixing member, and 
 
 wherein the first end face is located closer to the first fixing member than the second end face, in a state where the second printing process is being executed, 
 wherein the first nip forming member and the second nip forming member are made of rubber, and 
 wherein the first nip forming member is softer than the second nip forming member and located upstream of the second nip forming member in a direction of conveyance of the sheet. 
 
     
     
       12. An image forming apparatus including a fixing device, the fixing device comprising:
 a roller; 
 an endless belt; 
 a first pad having a first end face that faces the roller, and configured to nip the endless belt in combination with the roller; 
 a second pad having a second end face that faces the roller, and configured to nip the endless belt in combination with the roller; 
 a single holder configured to support the first pad and the second pad in such a manner that first pad and the second pad are moved together; 
 a heater; 
 a guide configured to support the holder in a manner that permits the first pad and the second pad supported by the holder to move with respect to the roller in a predetermined direction toward or away from the roller; 
 a spring configured to bias the holder toward the roller; and 
 a cam configured to move the holder in the predetermined direction; 
 wherein the image forming apparatus is capable of executing:
 a first printing process in which printing is performed with the holder located in a position where both of the first pad and the second pad nip the endless belt in combination with the roller, and 
 a second printing process in which printing is performed with the holder located in a position where the first pad nips the endless belt in combination with the first fixing member, but the second pad does not nip the endless belt in combination with the first fixing member, 
 
 wherein the first end face is located closer to the roller than the second end face, in a state where the second printing process is being executed and 
 wherein the first pad is softer than the second pad and located upstream of the second pad in a direction of conveyance of the sheet. 
 
     
     
       13. The image forming apparatus according to  claim 12 , wherein, in the first printing process, a biasing force of the spring is exerted on the first pad and the second pad, and
 wherein, in the second printing process, the biasing force of the spring is not exerted on the first pad and the second pad. 
 
     
     
       14. The image forming apparatus according to  claim 12 , wherein the fixing device further comprises a frame configured to support ends of the roller, and
 wherein the frame includes a groove as the guide, the groove being elongate in the predetermined direction. 
 
     
     
       15. The image forming apparatus according to  claim 12 , wherein the fixing device further comprises an arm configured to be rotatable, the arm being biased by the spring to press the holder against the roller. 
     
     
       16. The image forming apparatus according to  claim 15 , wherein the cam is configured such that:
 in a state in which the cam is not in contact with the arm, the holder is located in a position where both of the first pad and the second pad nip the endless belt in combination with the roller, and 
 in a state in which the cam is in contact with the arm, the holder is located in a position where the first pad nips the endless belt in combination with the roller, but the second pad does not nip the endless belt in combination with the roller. 
 
     
     
       17. The image forming apparatus according to  claim 16 , wherein the first printing process is performed in a state where the cam is not in contact with the arm, and
 wherein the second printing process is performed in a state where the cam is in contact with the arm. 
 
     
     
       18. The image forming apparatus according to  claim 12 , wherein the first pad and the seond pad are supported on the holder without a spring being positioned between the first pad and the holder and between the second pad and the holder. 
     
     
       19. The image forming apparatus according to  claim 12 , wherein the first pad and second pad are rectangular parallelepiped members. 
     
     
       20. The image forming apparatus according to  claim 12 , wherein the first pad is located apart from the second pad in a direction of conveyance of a sheet, and the first pad and the second pad are respectively biased toward directions away from each other by a holder spring.